SECOND OPINION; Genetic Test for Diabetes May Gauge Risk, but Is the Risk Worth Knowing?

By Denise Grady

Published: August 8, 2006

Like her mother and grandmother, my mother had Type 2 diabetes. For her, its most awful complication was artery disease, which caused innumerable mini-strokes, pinched off the circulation to her legs and ultimately ended her life.

My sisters and I hope to avoid her fate, or at least postpone it. Since obesity often brings on the disease in people with a family history like ours, we try to watch our weight.

Lately, I've been intrigued by the discovery of a gene variant that can predispose people to this type of diabetes, which usually develops in adults. Having the variant doesn't guarantee that you will get the disease, and lacking it doesn't guarantee that you won't. But it tells something about risk.

People who have one copy of the gene, inherited from one parent, have 1.4 times the risk of someone who lacks it, and those with two copies -- one from each parent -- have about twice the risk. People with the variants tend to make insufficient insulin, the hormone that lowers blood sugar.

The gene accounts for about 21 percent of all diabetes cases; more than a third of Americans carry one copy. Seven to 10 percent carry two.

Am I one of them? Do I want to find out? There is no way to do that yet, but Decode Genetics, the Icelandic company whose researchers found the gene variant, is planning to market a test, possibly by 2007 or 2008. It will probably cost hundreds of dollars, and be available only through doctors.

At first glance, testing doesn't seem to offer much to people like me. We already figure the deck is stacked against us. Even if the test came out negative, I would still suspect I was at risk, but from some other gene that hasn't been discovered yet.

Then again, if I tested positive, the threat would seem more real. Maybe I would eat less, exercise more, check my blood sugar more often, keep better track of risk factors for heart disease like cholesterol and blood pressure. I would also have to decide whether to inflict the information on my sons.

I'm not sure I want that straight-up shot of reality. Even with my family history, I figure there's a chance I got lucky and didn't inherit whatever my mother had. A test could erode that bit of optimism.

Dr. David Altshuler, a diabetes expert at Harvard who has studied the gene variants, said he thought offering a routine genetic test now would be premature.

He said the test would not help people who already know they are at risk because of their family histories or because they have impaired glucose tolerance, a condition that often leads to diabetes. They should already be trying to exercise and lose weight, or taking a medication to treat the glucose problem, he said.

''There may be people who would say, 'If I knew my risk was 50 percent instead of 30 percent, I would like to know that to make me try harder,' '' Dr. Altshuler said. ''You could argue that either of those is really high, and you should be trying hard already.''

He also cautioned that people who do get tested must keep in mind that a positive result does not seal their fate: their risk is higher, but not absolute. Similarly, those who test negative are not in the clear. If they have other risk factors they still have to be careful, because other genes are almost certainly involved in diabetes as well.

Dr. Richard Kahn, chief scientific and medical officer for the American Diabetes Association, had similar concerns and said the research was important, but, ''translating it into some practical action is a long ways away.''

Dr. Altshuler said another reason for his wariness is that ''there is another gold rush in this, in diagnostics.''

He praised Decode as first-rate in terms of science and ethics, but he said he worried about other companies looking to cash in on legitimate research by marketing questionable genetic tests directly to consumers.

''A lot of companies will push the idea of doing genetic testing -- 'You can have this done, we'll give you advice,' '' he said. ''I'm deeply concerned. Companies are pushing things that aren't valid, saying send us your DNA and we'll give you advice about lifestyle or diet based on your genetic profile. Very little is known, let alone anything with implications.'' But, he noted wryly, despite all his reservations he has not been able to talk his own mother out of wanting the genetic test for Type 2 diabetes.

The Federal Trade Commission is also concerned. Last month, its Web site carried a warning that there were no valid studies to support many genetic tests being marketed to consumers to gauge their disease risks or suggest they need dietary supplements or special diets.

Dr. Kari Stefansson, Decode's chief executive, said genetic tests that measure the probability of developing a disease ''are a new sort of information that our society is growing rapidly more accustomed to, but it is still not absolutely clear how we are going to use it.''

The first use of a Type 2 diabetes test, he said, would probably be in people with impaired glucose tolerance. Those who came out positive could be treated aggressively, perhaps with drugs. Those who tested negative could be offered a more conservative approach.

For people with a family history and normal glucose tolerance, Dr. Stefansson said, the best use of the test would be to test both the relative with diabetes and the concerned family member. If both tested positive, then the family member was at high risk and could try to do something about it.

What about people like me, whose diabetic relatives are long gone? I could be tested, he said, and if I had the risky variant it might be a warning sign. But if I didn't have it, I still wouldn't be out of the woods.

So what do I want to do? Right now, I'm leaning toward having the test if it becomes available. I'm not sure what I'd do with the results or whether they would mean anything for my future. But I'd like the information, and the right to decide for myself whether to act on it.